The present invention relates to pistons for internal combustion engines and more particularly to light metal pistons, for example aluminium or aluminium alloy pistons.
In the design and nanufacture of pistons for internal combustion engines, a great deal of care is taken to provide sufficient running clearances for the pistons under all forseeable engine operating conditions and in particular arrangements are made for adequate cooling and lubrication of the piston during its operation. Nevertheless, failure of the cooling or lubrication facilities, or the malfunction of some other component, may still result in seizure of a piston in an engine. Particularly in cases such as high speed marine engines or in locomotives, where the engines have a large number of cylinders and the operator or driver is situated remote from the engine compartment, in the event of seizure of a piston the engine may continue to run on full power from the remaining cylinders until the seized piston and/or the associated cylinder liner is largely broken up, resulting in very serious damage to the engine.
In order to reduce the possibility of such damage resulting from piston seizure, particularly in the types of situations mentioned above, it has been proposed to employ forged aluminium pistons since they have a greater ductility than cast pistons and therefore a forged material can be said to lessen the danger of piston breakage before an engine can be stopped in the case of some failure, such as in the cooling or lubrication systems. However, when designing an engine it is not always possible to meet the requirements for wear-resistance and adequate piston cooling where forged pistons are employed.
It is accordingly an object of the present invention to provide improved constructions of cast light metal piston.